mm/gup: use gup_can_follow_protnone() also in GUP-fast

There seems to be no reason why FOLL_FORCE during GUP-fast would have to
fallback to the slow path when stumbling over a PROT_NONE mapped page.  We
only have to trigger hinting faults in case FOLL_FORCE is not set, and any
kind of fault handling naturally happens from the slow path -- where NUMA
hinting accounting/handling would be performed.

Note that the comment regarding THP migration is outdated: commit
2b4847e73004 ("mm: numa: serialise parallel get_user_page against THP
migration") described that this was required for THP due to lack of PMD
migration entries.  Nowadays, we do have proper PMD migration entries in
place -- see set_pmd_migration_entry(), which does a proper
pmdp_invalidate() when placing the migration entry.

So let's just reuse gup_can_follow_protnone() here to make it consistent
and drop the somewhat outdated comments.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Peter Xu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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